The relationship between psoriasis and associated diseases has drawn particular interest in recent years. To provide appropriate management of psoriasis from an early stage, it is necessary to include prompt diagnosis of concomitant disease and to prevent and treat any comorbidity found. Such an integrated approach also serves to ensure that the drugs used to treat associated diseases do not interfere with the management of psoriasis, and vice versa. This clinical practice guideline on the management of comorbidity in psoriasis has been drawn up to help dermatologists to achieve an integrated approach to this inflammatory disease. The guide focuses primarily on the diseases most often found in patients with psoriasis, which include psoriatic arthritis, cardiovascular disease, nonalcoholic fatty liver disease, inflammatory bowel disease, lymphoma, skin cancer, anxiety, and depression. Cardiovascular disease is approached through the study of its major risk factors (obesity, diabetes mellitus, hypertension, dyslipidemia, and metabolic syndrome). Other cardiovascular risk factors related to lifestyle, such as smoking and alcohol consumption, are also discussed. The overall aim of this guide is to provide the dermatologist with a precise, easy to-use tool for systematizing the diagnosis of comorbidity in these patients and to facilitate decisions regarding referral and treatment once associated diseases have been found. The specific objectives are as follows: a) to review the most common diseases associated with psoriasis, including the prevalence of each one and its importance to the dermatologist; b) to provide guidelines for the physical examination, diagnostic tests, and clinical criteria on which to base a preliminary diagnosis; c) to establish criteria for the appropriate referral of patients with suspected comorbidity; d) to provide information on how therapies for psoriasis may modify the course of associated diseases, and e) to provide information concerning treatments prescribed for associated diseases that may have an impact on the course of psoriasis. This guide has been written by a working group of guideline methodologists and clinical experts. The selection of the diseases included was based on a systematic review of the literature and a summary of available evidence; information on the prevalence of each comorbidity was also taken from the literature. The recommendations on diagnostic criteria are based on the main clinical practice guidelines for each of the diseases discussed and on the recommendations of the expert advisory group. The information regarding the repercussions of psoriasis treatments on comorbid diseases was obtained from the summary of product characteristics of each drug. The statements concerning the impact on psoriasis of the associated diseases and their treatment are based on the review of the literature.